The present invention teaches a process for preparing strip stock from aluminum and aluminum alloys, preferbly Al-Mg-Mn alloys, by means of strip casting machines, wherein the strip exhibits low earing properties and is suitable for use in the manufacture of deep drawn and ironed hollow articles such as cans or the like.
In recent years Al-Mg-Mn alloys, in the form of cold rolled strip, have been successfully processed into beverage cans by deep drawing and ironing. A number of processes are known for the production of aluminum strip for use in these beverage cans. Typically, aluminum is cast by known methods such as horizontal and vertical direct chill casting, or strip casting for further treatment. One such known process is disclosed in U.S. Pat. No. 3,787,248 to Setzer et al. and assigned to the Assignee of the present invention. The process comprises casting an Al-Mg-Mn alloy, homogenizing this alloy at a temperature of between 455.degree. C. to 620.degree. C. for 2 to 24 hours, hot rolling from a starting temperature of 345.degree. C. to 510.degree. C. with a total reduction in thickness of at least 20%, subsequent rolling, starting from a temperature of 205.degree. C. to 430.degree. C. with reduction of at least 20%, subsequent rolling, starting from a temperature of less than 205.degree. C. with reduction of at least 20%, heating the alloy between 95.degree. C. and 230.degree. C. for at least 5 seconds but no longer than a time determined by the equation T(10+log t)=12,500, T standing for degrees Kelvin and t for maximum time in minutes.
While the process disclosed in the aforenoted patent has been used successfully for making metal strip to be used in the manufacture of cans, it has been found that strip produced by said process is not completely satisfactory in that the material experiences a high degree of earing.
A further known process for the production of strip is disclosed in Light Metal Age, Volume 33, 1975, December, Pages 28-33. In the aforenoted article the strip was prepared by a strip casting process and was thereafter treated so as to be useful in the manufacture of cans. One basic problem which arises in the production of strip via strip casting machines as disclosed in the above-noted article is that the dendritic arm spacing or cell size at the surface of the strip is too large. As a result of this large dendritic arm spacing, the strip exhibits extensive surface porosity which leads to cracks in the final rolled strip. In addition, when the dendritic arm spacing is too large, there is a danger of surface segregation which can lead to poor quality in the final rolled strip which in turn causes difficulties during the drawing and ironing operation.
Accordingly, it is a principal object of the present invention to provide a process for preparing aluminum alloy strip stock by means of a continuous strip casting machine which exhibits properties favorable for further processing by cold rolling.
It is a further object of the present invention to provide an improved process for cold rolling continuous strip cast stock to thereby improve the earing properties thereof.
It is still a further object of the present invention to provide the process as aforesaid which enables the aluminum alloy strip to be used in the production of cans and the like.
Further objects and advantages will appear hereinbelow.